Assessing components of the natural environment of the Upper ...

More documents

Recommendations

Info

30 S. Lang et al.: Assessing components of the natural environment Figure 7. Land use/land cover classification for the Wang Chu river basin (Bhutan). Figure 8. Land use/land cover classification for the Salzach river basin (Austria/Germany). Adv. Sci. Res., 7, 21–36, 2011 www.adv-sci-res.net/7/21/2011/
S. Lang et al.: Assessing components of the natural environment 31 Table 5. Combined parameters and weights for DRASTIC modelling. Depth to Recharge Aquifer Soil Terrain Impact of Conductivity groundwater media properties slope vadose zone [m] rate [mm y −1 ] rate [category] rate [category] rate [%] rate [category] rate [m s −1 ] rate 0–5 10 5–104 1 weath. metamorphic 3 clay 1 0–2 10 silt/clay 1 4.17E-09–4.17E-07 1 5–10 9 104–161 3 metamorphic 8 clayey silt 3 2–6 9 shale 3 4.17E-07–1.25E-06 2 161–278 6 metamorphic/igneous 4 silt 4 6–12 5 limestone 6 1.25E-06–2.92E-06 4 278–398 8 sedimentary 8 fine sand 6 12–18 3 sandstone 6 2.92E-06–4.17E-06 6 396–1350 9 medium sand 8 > 18 1 sand/gravel 8 4.17E-06–8.34E-06 8 coarse sand 9 basalt 9 >8.34E-06 10 gravel 10 limestone 10 a recent study on groundwater resources of India (Chatterjee and Purohit, 2009). The precipitation data were interpolated using natural neighbourhood approach to provide zones comparable with recharge zones by Chatterjee and Purohit (2009). Based on these data sources there were modified recharge zones determined to be compared with groundwater draft zones (Chatterjee and Purohit, 2009) and to provide source data for both DRASTIC and groundwater availability investigation. Table 6. DRASTIC index values. parameter weight vulnerability DRASTIC index values depth to groundwater 5 very low 87–217 net precipitation 4 Low 217–348 aquifer media 3 moderate 348–478 soil media 2 High 478–609 terrain slope 1 very high 609–740 4.4.3 Aquifer and soil media According to a study on groundwater resources of India (Chatterjee and Purohit, 2009) there were 4 prevailing groups of aquifers determined: (1) Alluvium: Describes the quaternary sediments surrounding the Brahmaputra river basin, highest permeability of all the present aquifers; (2) Extensive alluvium: Tertiary and quaternary sediments in the main area of Assam, stretching from Shillong Plateau eastwards to Jorhat and southwards to Cachar; (3) Crystalline rocks: Proterozoic massifs in the region of North Cachar Hills, Igneous and Metamorphic rocks; (4) Aquifer in hilly areas: Consists of Igneous and Metamorphic rocks in the districts of Lakhimpur, Dhemaji, Dibrugarh and Sonitpur. All the three DRASTIC categories concerning soil properties derived from Assam soil map (Sehgal et al., 1987). There are soil groups mapped and referenced to describe prevailing texture categories. The soil classification is based on USDA system. The only used value is the DRASTIC rating itself. The analyses are based on relative texture classification, related to texture categories. Compiled data are converted to DRASTIC rated layers and all the parameters consequently combined (see Table 5). The interpretation is based on DRASTIC INDEX (DI) weighting formula and corresponding indicators of aquifer vulnerability are determined by weighted sum. The output coverage contains graphical representation based on raster data analysis corresponding to DI values (see Fig. 9). The output features have the attribute from the original feature from the input coverage and the feature in the intersect coverage, which they intersect. The values for the final index’s, i.e. “Low,” “Medium,” etc., were created by first applying the Jenk’s Natural Breaks classification for all regions into five classes, then taking the average for each class and applying the same values to all regions to be consistent across the entire region. The used rating is therefore applicable for the situation of Assam only as the classes were set on relative range of DI values (Table 6). 4.5 Eco-hydrology and wetland characteristics The Assam part of the Brahmaputra catchment is characterized by three terrestrial eco-regions within the Tropical and Subtropical Moist Broadleaf Forests biome, of which the Brahmaputra Valley semi evergreen forest eco-region has the highest proportion within the river corridor. The river-scape in the Assam river valley provides low ecosystem services in contrast to the slopes and hills, due to the fact that lower elevations showed higher proportions of arable land and built up areas. These LULC-classes are the main driving forces for pollution. Natural environment and ecosystem services information are relevant for the further processing by the social science groups, providing indicators to be linked with socio-economic models. Local scale and River Basin scale were combined by a rule-based expert system at sub-catchment scale, which uses the LULC classification and the NDVI as basis to identify alluvial areas, lakes, alpine swamps and meadows, floodplains and beels – typical lake-like water bodies of different size in close connection with the river, in Assam and Bhutan. These different wetland classes were further differentiated www.adv-sci-res.net/7/21/2011/ Adv. Sci. Res., 7, 21–36, 2011
Page 1 and 2: Open Sciences Adv. Sci. Res., 7, 21
Page 3 and 4: S. Lang et al.: Assessing component
Page 9: S. Lang et al.: Assessing component

Assessing components of the natural environment of the Upper ...

Create successful ePaper yourself

Delete template?

Save as template?